Method of forming thin film transistor substrate

ABSTRACT

A thin film transistor substrate and a fabricating method thereof wherein a contacting size between an electrode and an active layer can be reduced to provide a small and light panel. In the thin film transistor substrate, a conductive layer is formed on the substrate. A first insulating layer for insulating the conductive layer overlies the conductive layer. A second insulating layer this is different from the first insulating layer overlies the first insulating layer. A third insulating layer overlies the second insulating layer. A contact through the first, second, and third insulating layers exposes a portion of the conductive layer and has a trapezoidal section. An electrode is connected to the conductive layer and overlies a portion of an inclined face of the contact hole. The inclined face of the contact hole includes a protrusion formed by a portion of the second insulating layer and creates an overhang structure.

The present application is a divisional of U.S. patent application Ser.No. 11/152,960, filed Jun. 15, 2005 now U.S. Pat. No. 7,262,454.

This application claims the benefit of Korean Patent Application No.P2004-100071 filed in Korea on Dec. 1, 2004, which is herebyincorporated by reference.

BACKGROUND

1. Technical Field

This invention relates to a thin film transistor substrate and afabricating method thereof, and more particularly to a thin filmtransistor substrate and a fabricating method thereof wherein a contactsize between an electrode and an active layer can be reduced to providea small and light panel.

2. Description of the Related Art

Generally, a liquid crystal display (LCD) allows each liquid crystalcell that is arranged on a liquid crystal display panel in a matrix tocontrol the light transmittance in accordance with a video signal,thereby displaying a picture.

In each liquid crystal cell, a thin film transistor (TUFT) is used as aswitching device for supplying a video signal independently. An activelayer of such a TUFT employs an amorphous silicon (amorphous-Si) orpolycrystalline silicon (poly-Si). Herein, when the poly-Si is used, adriving circuit requiring a high response speed can be built in theliquid crystal display panel because the poly-Si has approximatelyhundred times faster charge mobility than the amorphous-Si.

FIG. 1 schematically shows a liquid crystal display panel employing aconventional poly-TUFT.

Referring to FIG. 1, the liquid crystal display panel includes a picturedisplay part 96, a data driver 92 for driving a data line 4 of thepicture display part 96, and a gate driver 94 for driving a gate line 2of the picture display part 96.

The picture display part 96 has liquid crystal cells CL arranged in amatrix to display a picture. Each of the liquid crystal cells CLincludes a TUFT 30 connected to the gate line 2 and the data line 4. TheTUFT 30 charges a video signal from the data line 4 into the liquidcrystal cell CL in response to a scanning signal from the gate line 2.In response to the charged video signal, the liquid crystal cell CLreacts a liquid crystal having a dielectric anisotropy to control lighttransmittance, thereby implementing a gray level.

The gate driver 94 sequentially drives the gate line 2. The data driver92 applies a video signal to the data line 4 whenever the gate line 2 isdriven.

Such a liquid crystal display panel is formed by joining a TUFTsubstrate, provided with the data driver 92 and the gate driver 94 alongwith the TUFT 30 of the liquid crystal cell CL, to a color filtersubstrate provided with a common electrode and a color filter, etc. witha liquid crystal therebetween.

FIG. 2 is a partial plan view of a picture display part of the TUFTsubstrate included in the liquid crystal display panel shown in FIG. 1,and FIG. 3 is a section view of the TUFT substrate taken along sectionline III-III of FIG. 2.

Referring to FIG. 2 and FIG. 3, the picture display part of the TUFTsubstrate includes a TUFT 30 connected to the gate line 2 and the dataline 4, and a pixel electrode 22 connected to the TUFT 30. The TUFT 30may be formed as an N-type or P-type TUFT, but the TUFT 30 formed as anN-type only will be described below.

The TUFT 30 charges a video signal into the pixel electrode 22. To thisend, the TUFT 30 includes a gate electrode 6 connected to the gate line2, a source electrode included in the data line 4, and a drain electrode10 connected via a pixel contact hole 20 passing through the pixelelectrode 22 and the protective film 18. The gate electrode 6 overlapswith a channel area 14C of the active layer 14 provided on a buffer film16 with having a gate insulating film 12 therebetween. The sourceelectrode and the drain electrode 10 are formed in such a manner to beinsulated from the gate electrode 6 with having an interlayer insulatingfilm 26 therebetween. Further, the source electrode and the drainelectrode 10 are connected, via a source contact hole 24S and a draincontact hole 24D passing through the interlayer insulating film 26 andthe gate insulating film 12, to a source area 14S and a drain area 14Dof the active layer 14, which are doped with an n⁺ impurity,respectively. The active layer may include a lightly doped drain (LDD)area (not shown) doped with an n⁻ impurity between the channel area 14Cand the source and drain areas 14S and 14D in order to reduce an offcurrent.

A formation of the contact hole 24 and the electrode 10 on such apoly-TUFT substrate will be described with reference to FIG. 4A to FIG.4C below.

Firstly, referring to FIG. 4A, in the poly-TUFT substrate, the bufferfilm 16 is formed on a lower substrate 1 and then the active layer 14 isformed on the buffer film 16. Further, the gate insulating film 12 isformed at the upper portion of the active layer 14 and then theinterlayer insulating film 26 is formed thereon.

The active layer 14 is formed by depositing amorphous-Si on the lowersubstrate 1 and then crystallizing it by a laser into a poly-Si; andthereafter by patterning it by a photolithography and etching processusing a mask.

The gate insulating film 12 is formed by entirely depositing aninorganic insulating material such as SiO₂, and the like.

The interlayer insulating film 26 is formed by blanket depositing aninorganic insulating material such as SiO₂, and the like on the gateinsulating film 12.

Referring to FIG. 4B, the interlayer insulating film 26 and the gateinsulating film 12 have a contact hole 24 formed therethrough aphotolithography and etching process. More specifically, in thephotolithography process, the photo-resist pattern is formed by coatinga photo-resist onto the interlayer insulating film 26; and thenpartially exposing to light by arranging a patterned mask at the upperportion of the photo-resist and developing the photo-resist. Thereafter,the contact hole 24 is formed by dry etching and wet etching. Thecontact hole 24 formed in this manner has a slope, and a section thereofis formed in a trapezoidal shape.

Referring to FIG. 4C, the electrode 10 is deposited onto the surface ofthe contact hole 24 using a mask. In this case, the electrode 10 isformed in such a manner to cover the entire surface of the contact hole24 and the peripheral of the aperture of the interlayer insulating film26.

In reality, when the contact hole 24 connected to the active layer 14 isdesigned to have a size of 4 μm, a size of the upper contact hole 24provided at the aperture on the interlayer insulating film 26 becomesabout 7 μm and the width of the electrode 10 becomes 11 μm.

As described above, the conventional electrode 10 has a problem in that,since it is formed in such a manner to cover the whole portion of uppercontact hole 24 provided at the aperture of the interlayer insulatingfilm 26, it has a large width. Accordingly, there has been suggested ascheme of maximizing a slope of the contact hole 24 in order to reduce asize of the contact hole 24. However, when a slope of the contact hole24 is maximized, there is a problem in that an electrode 10 a, providedat the periphery of the aperture of the interlayer insulating film 26,and an electrode 10 b, provided at the contact hole 24, not connected toeach other, as shown in FIG. 5. Also, it is necessary to use a wetetching process for the purpose of protecting the active layer 14 whenthe contact hole 24 is formed. Thus, the contact hole 24 has a slopethat is greater than a desired angle, which causes a problem inmaximizing a slope of the contact hole 24. Such a formation of thecontact hole fails to satisfy the need for a small size contact hole 24,which is required for a small-dimension and light-weight panel.

BRIEF SUMMARY

Accordingly, it is an object of the present invention to provide a thinfilm transistor substrate and a fabricating method thereof wherein thecontact size between an electrode and an active layer can be reduced toprovide a small and light panel.

In order to achieve these and other objects of the invention, a thinfilm transistor substrate according to one aspect of the presentinvention includes a substrate and a conductive layer overlying thesubstrate. A first insulating layer for insulating the conductive layeroverlies the conductive layer and a second insulating layer comprising amaterial different from the first insulating layer overlies the firstinsulating layer. A third insulating layer overlies the secondinsulating layer. A contact through the first, second, and thirdinsulating layers exposes a portion of the conductive layer and having atrapezoidal section, and an electrode is connected to the conductivelayer and overlies a portion of an inclined face of the contact hole.The inclined face of the contact hole includes a protrusion formed by aportion of the second insulating layer and creating an overhangstructure.

In the thin film transistor substrate, wherein the first and thirdinsulating layers are made from an inorganic insulating material such asSiO₂, and a material of the second insulating layer has a good adhesiveforce to a metal and is an inorganic insulating material, such asSiN_(x), different from the third insulating layer.

Herein, a size ratio of the bottom of the contact hole to the top of thecontact hole to the top of the electrode is about 3˜5:8˜10:7˜9.

A method of fabricating a thin film transistor substrate according toanother aspect of the present invention includes the steps of providinga substrate and forming a conductive layer on the substrate; forming afirst insulating layer for insulating the conductive layer on theconductive layer; forming a second insulating layer on the firstinsulating layer on the first insulating layer, wherein the secondinsulating layer comprises a material different from the firstinsulating layer; forming a third insulating layer on the secondinsulating layer; forming a contact through the first, second, and thirdinsulating layers to expose a portion of the conductive layer and havinga trapezoidal section; forming an electrode connected to the conductivelayer and partially provided on an inclined face of the contact hole;and providing a protrusion creating an overhang structure at one side ofan inclined face of the contact hole.

In the method, said step of providing the protrusion includes etchingthe third insulating layer by at least one of a dry etching and a wetetching; etching the second insulating layer by at least one of said dryetching and said wet etching; and etching the first insulating layer bysaid wet etching.

Herein, the second insulating layer is etched using both the dry etchingmethod and the wet etching method. A ratio of a number of times the dryetching method is used to a number of times the wet etching method isused is about 80˜50:20˜50.

In the method, said etchant liquid used in said wet etching is selectedfrom at least one of a buffered oxide etchant (BOE) and a buffered —HF,and an etchant gas used in said dry etching is selected from at leastone of SF₆ and CF₄.

In the method, the first and third insulating layers are made from aninorganic insulating material such as SiO₂, and a material of the secondinsulating layer has a good adhesive force to a metal and is aninorganic insulating material, such as SiN_(x), different from the thirdinsulating layer.

A thickness of the second insulating layer is greater than about 500 Åand less than about 1.5 times of the thickness of the first insulatinglayer.

A liquid crystal display according to one aspect of the presentinvention includes a thin film transistor having an active region and afirst, second and third insulating layers sequentially overlying thethin film transistor. The second insulating layer comprises a materialdifferent from the first insulating layer. A contact opening through thefirst, second, and third insulating layers exposes a portion of theactive region. An electrode is connected to the active region andoverlies only a portion of an inclined face of the contact hole. Theelectrode has a characteristic dimension that is less than acharacteristic dimension of the contact opening at an upper surface ofthe third insulating layer, but greater than a characteristic dimensionof the contact opening at the active region.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects of the invention will be apparent from thefollowing detailed description of the embodiments of the presentinvention with reference to the accompanying drawings, in which:

FIG. 1 is a schematic view showing a structure of a conventional liquidcrystal display employing a poly silicon;

FIG. 2 is a fractional plan view of a picture display part of the thinfilm transistor substrate included in the liquid crystal display panelshown in FIG. 1;

FIG. 3 is a section view of the TUFT substrate taken along section linesIII-III′ of FIG.2;

FIG. 4A to FIG. 4C are section views for explaining a method offabricating the thin film transistor substrate shown in FIG. 3 step bystep;

FIG. 5 depicts a breakage of the electrode provided at the conventionalcontact hole;

FIG. 6 is a fractional plan view of the thin film transistor substrateaccording to a first embodiment of the present invention;

FIG. 7 is a section view of the thin film transistor substrate takenalong the VII-VII′ line in FIG. 6;

FIG. 8A to FIG. 8C are section views for explaining a method offabricating the thin film transistor substrate according to the firstembodiment of the present invention step by step;

FIG. 9 is a fractional plan view of the thin film transistor substrateaccording to a second embodiment of the present invention;

FIG. 10A to FIG. 10C are section views for explaining a method offabricating the thin film transistor substrate according to the secondembodiment of the present invention step by step; and

FIG. 11A to FIG. 11C are section views for explaining a method offabricating the thin film transistor substrate shown in FIG. 10B step bystep.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

Hereinafter, the preferred embodiments of the present invention will bedescribed in detail with reference to FIGS. 6 to 11.

FIG. 6 is a fractional plan view of the thin film transistor substrateaccording to a first embodiment of the present invention; and FIG. 7 isa section view of the thin film transistor substrate taken along theVII-VII′ line in FIG. 6.

Referring to FIG. 6 and FIG. 7, the TUFT substrate includes a TUFT 130connected to a gate line 102 and a data line 104, and a pixel electrode122 connected to the TUFT 130. The TUFT 130 may be formed in as anN-type or P-type TUFT, but the TUFT 130 formed as an N-type only will bedescribed below.

The TUFT 130 charges a video signal into the pixel electrode 122. Tothis end, the TUFT 130 includes a gate electrode 106 connected to thegate line 102, a source electrode included in the data line 104, a pixelcontact hole 120 passing through a protective film 118, a drainelectrode 110 connected, via the pixel contact hole 120, to the pixelelectrode 122, and an active layer 114 for forming a channel between thesource electrode and the drain electrode 110 by the gate electrode 106.

The active layer 114 is provided on a lower substrate 101 with a bufferfilm 116 therebetween. The gate electrode 106 connected to the gate line102 overlaps a channel area 114C of the active layer 114 with a gateinsulating film 112 therebetween. The data line 104 and the drainelectrode 110 are formed in such a manner to be insulated from the gateelectrode 106 by an interlayer insulating film 126. Further, the sourceelectrode, included in the data line 104, and the drain electrode 110are connected, via a source contact hole 124S and a drain contact hole124D passing through the interlayer insulating film 126 and the gateinsulating film 112, to a source area 114S and a drain area 114D dopedwith an n⁺ impurity, respectively. The active layer 114 may furtherinclude a lightly doped drain (LDD) area (not shown) doped with an n⁻impurity between the channel area 114C and the source and drain areas114S and 114D in order to reduce an off current. Herein, the sourceelectrode and the drain electrode 110 and the pixel electrode 122 formedthrough the respective contact holes 120, 124S and 124D have smallerwidths than upper hole sizes of the contact holes 120, 124S and 124D.

A formation process of the source electrode and the drain electrode 110going through the source drain contact holes 124S and 124D according tothe first embodiment of the present invention having the above-mentionedstructure will be described with reference to FIG. 8A to FIG. 8C below.

Firstly, referring to FIG. 8A, in the TUFT substrate according to thefirst embodiment of the present invention, the buffer film 116 isblanket deposited onto the lower substrate 101, and the active layer 114is formed on the buffer film 116. Further, the gate insulating film 112is formed on the upper portion of the active layer 114 and then theinterlayer insulating film 126 is formed thereon.

The active layer 114 is formed by depositing amorphous-Si on the lowersubstrate 101 and then crystallizing it by a laser into a poly-Si; andthereafter by patterning it by a photolithography and etching processusing a mask.

The gate insulating film 112 is formed by blanket depositing aninorganic insulating material such as Sio₂, and the like.

The interlayer insulating film 126 is formed by entirely depositing aninorganic insulating material such as Sio₂, and the like onto the gateinsulating film 112.

Referring to FIG. 8B, the interlayer insulating film 126 and the gateinsulating film 112 has a contact hole 124 formed therethrough by aphotolithography and etching process. This contact hole 124 forms a slowinclination angle by controlling the ratio of dry etching to wetetching. More specifically, an etching process is performed having arate with at a ratio of dry etching to wet etching corresponding toabout 80˜50:20˜50, and preferably about 60:40. By carrying out such anetching process, a low inclination angle of the contact hole 124 isachieved according to the first embodiment of the present invention.

Referring to FIG. 8C, the electrode 110 is deposited onto the surface ofthe contact hole 124 using a mask. In this case, a size of the maskpattern is set to have a smaller value than a characteristic dimensionof the contact hole 124 at the upper surface of the insulating film 126,Thus, the electrode 110 is formed on one side of both the inclinedsurface of the contact hole 124 and the lower portion of the contacthole 124. In this case, a width of the electrode 110 is set to be lessthan a characteristic dimension of the contact hole 124 at the top andgreater than the size of the contact hole 124 at the bottom.

In one exemplary embodiment, when the lower hole size of the contacthole 124 is designed to have a dimension of about 4 μm, the upper holedimension size of the contact hole 124 is about 9 μm and a total lengthof the width of the electrode 110 is about 8 μm. Accordingly, a width ofthe electrode 110 connected, via the contact hole 124, to the activelayer 114 is reduced.

Referring back to FIGS. 6 and 7, since the pixel electrode 122 goingthrough a pixel contact hole 120 can be formed by the same process asthe formation process of the source contact hole 124S and the draincontact hole 124D, an explanation as to it will be omitted.

Since the TUFT substrate according to the first embodiment of thepresent invention having the above-mentioned structure is formed suchthat an adhesive force between the electrode 110 and the contact hole124 may be weak, there is a possibility that an etchant liquid used inthe etching process to form the electrode 110 can infiltrate into theactive layer 114 and cause substrate defects. Accordingly, a secondembodiment of the present invention provides a structure in whichinfiltration of the etchant liquid can be prevented when the electrodeis formed in the contact hole.

FIG. 9 shows a TET substrate including a TUFT 230 connected to a gateline (not shown) and a data line 204, and a pixel electrode 222connected to the TUFT 230. A drain electrode 210 is connected to anactive layer 214 through the contact hole 224 according to the secondembodiment of the present invention. A pixel contact hole 220 passesthrough a protective film 218 and exposes portion of the drain electrode210. The drain electrode 210 is connected, via the pixel contact hole120, to the pixel electrode 222. An active layer 214 forms a channel214C between a source region 214S and a drain region 214D. A gateelectrode 206 overlies the channel region 214C and is separatedtherefrom by a portion of a gate insulating film 212. The data line 204is connected to a source region 214S through a source contact hole 224Sand the drain electrode 210 is connected to the drain region 2140through a drain contact hole 214D.

A formation process of the contact hole 224 and the electrode 210 goingthrough the contact hole 224 according to the second embodiment of thepresent invention shown in FIG. 9 will be described in detail withreference to FIG. 10A to FIG. 10C below.

Referring to FIG. 10A, in the TUFT substrate according to the secondembodiment of the present invention, the buffer film 216 is blanketdeposited onto the lower substrate 201, and the active layer 214 isformed on the buffer film 216. Further, the gate insulating film 212 isformed on the upper portion of the active layer 214 and then anauxiliary insulating film 228 having a different material from the gateinsulating film 212 is formed on the gate insulating film 212.Thereafter, the interlayer insulating film 226 is formed thereon.

The active layer 214 is formed by depositing amorphous-Si on the lowersubstrate 101 and then crystallizing it by a laser into a poly-Si; andthereafter by patterning it by a photolithography and etching processusing a mask.

The gate insulating film 112 is formed by blanket depositing aninorganic insulating material such as SiO₂, and the like.

The auxiliary insulating film 228 is formed by blanket depositing aninorganic insulating material different from the gate insulating film212, such as SiN_(x), and the like.

The interlayer insulating film 226 is formed by blanket depositing aninorganic insulating material such as Sio₂, and the like onto the gateinsulating film 212.

Referring to FIG. 10B, the interlayer insulating film 226 and the gateinsulating film 212 has a contact hole 224 formed therethrough by aphotolithography and etching process. This contact hole 224 is formed tohave a low inclination angle by controlling the ratio of dry etching towet etching. More specifically, the interlayer insulating film 226 isetched by a dry etching process and a wet etching process as shown inthe process sequence illustrated FIGS. 11A-11C. Herein, the ratio of dryetching to wet etching can be set differently depending upon thethickness of the interlayer insulating layer 226. In order to reduce thesize of the contact hole 224, it is preferable that the dry etching rateis higher. In this case, an etching speed is different because theinterlayer insulating film 226 and the auxiliary insulating film 228 aremade from different materials. The etching of the interlayer insulatingfilm 226 progresses faster than that of the auxiliary insulating film228. Thus, the structure of the contact hole 224 takes a stepwise shapeas shown in FIG. 11B when the auxiliary insulating film 228 is etchedonly by the wet etching process, whereas it takes a shape as shown inFIG. 11C when the auxiliary insulating film 228 is etched by the dryetching process. Finally, the gate insulating film 212 is etched only bythe wet etching process. In this case, the wet etching of the gateinsulating film 212 progresses faster than that of the auxiliaryinsulating film 228, so that a protrusion is created by the auxiliaryinsulating film 228 that forms an overhang structure and the contacthole 224 has a low inclination angle. Herein, sizes of the protrusionsof the auxiliary insulating films 228 formed in accordance with theprocesses of FIG. 11B and FIG. 11C are set differently. In other words,the length of the protrusion formed in the process of FIG. 11B is set tohave a larger value than the protrusion formed in the process of FIG.11C. Thus, an etching process of the auxiliary insulating film 228 haspreferably a ratio of dry etching to wet etching corresponding to about50˜70:50˜30, and more preferably a ratio of approximately 60:40.

Referring to FIG. 10C, the electrode 210 is deposited onto the surfaceof the contact hole 224 using a mask. In this case, a size of the maskpattern is set to have a smaller value than an upper hole size of thecontact hole 224. Thus, the electrode 210 is formed on one side of boththe inclined surface of the contact hole 224 and a lower portion of theof the contact hole 224. In this case, a width of the electrode 210 isset to be less than a characteristic dimension in the upper region ofthe contact hole 224 and greater than a characteristic dimension at thebottom of the contact hole 224. Herein, the protrusion provided on theinclined face of the contact hole 224 is SiN_(x), which has stronglyadheres to the electrode 210, so that it can prevent an infiltration ofthe etchant liquid. Also, the inclined face of the contact hole 224 hasa protrusion forming an overhang structure, so that it can furtherprevent an infiltration of the etchant liquid. The thickness of SiN_(x)must be enough to ensure an adhesive force, and is formed to havethickness ranging from more than about 500 Å to less than about 1.5times the thickness of the gate insulating film 212.

Meanwhile, a type of the etchant liquid used in the formation processaccording to the first and second embodiment of the present inventionincludes buffered oxide etch (BOE) and Buffered-HF, and the like, andthe etchant gas includes SF₆ and CF₄, and the like.

As described above, according to the present invention, the electrode incontact with the active layer through one side of the inclined face ofthe contact hole and the bottom of the hole can be provided to reducethe width of the electrode. Accordingly, it becomes possible to realizea reduction of the contact face of the electrode formed through thecontact hole in order to provide a small-size and light-weight panel.Furthermore, it becomes possible to prevent an infiltration of theetchant liquid. occurring upon formation of the electrode and henceprevent substrate defects.

Although the present invention has been explained by the embodimentsshown in the drawings described above, it should be understood to theperson of ordinary skill in the art that the invention is not limited tothe illustrative embodiments, but rather that various changes ormodifications thereof are possible without departing from the spirit ofthe invention. Accordingly, the scope of the invention shall bedetermined only by the appended claims and their equivalents.

1. A method of fabricating a thin film transistor substrate comprisingthe steps of: providing a substrate; forming an active layer on thesubstrate; forming a first insulating layer for insulating the activelayer on the substrate; forming a second insulating layer on the firstinsulating layer, wherein the second insulating layer comprises amaterial different from the first insulating layer; forming a thirdinsulating layer on the second insulating layer; forming a contact holethrough the first, second, and third insulating layers to expose aportion of the active layer; forming an electrode connected to theactive layer and provided on only a portion of an inclined face of thecontact hole; and providing a protrusion creating an overhang structureat one side of an inclined face of the contact hole.
 2. The method asclaimed in claim 1, wherein said step of providing the protrusioncomprises: etching the third insulating layer by at least one of a dryetching method or a wet etching method; etching the second insulatinglayer by at least one of the dry etching method or the wet etchingmethod; and etching the first insulating layer by the wet etchingmethod.
 3. The method as claimed in claim 2, wherein the firstinsulating layer is etched only by the wet etching method.
 4. The methodas claimed in claim 2, wherein the wet etching method comprises at leastone of: etching the third insulating layer using a first etchant oretching the second insulating layer using a second etchant.
 5. Themethod as claimed in claim 4, wherein the wet etching method furthercomprises etching the first insulating layer using the first etchant. 6.The method as claimed in claim 2, wherein the wet etching methodcomprises etching the third insulating layer and second insulating layerusing a first etchant.
 7. The method as claimed in claim 6, wherein thewet etching method further comprises etching the first insulating layerusing the first etchant.
 8. The method as claimed in claim 2, whereinthe second insulating layer is etched using both the dry etching methodand the wet etching method, and a ratio of a number of times the dryetching method is used to a number of times the wet etching method isused is about 80˜50:20˜50.
 9. The method as claimed in claim 2, whereinan etchant liquid used in the wet etching method comprises at least oneof a buffered oxide etchant (BOE) or a buffered HF, and an etchant gasused in the dry etching process comprises at least one of SF₆ or CF₄.10. The method as claimed in claim 1, wherein the first and thirdinsulating layers comprise an inorganic insulating material, and thesecond insulating layer comprises an inorganic insulating materialhaving good adhesive force to a metal and that is different from thethird insulating layer.
 11. The method as claimed in claim 10, whereinthe first and third insulating layers comprise SiO₂ and the secondinsulating layer comprises SiN_(x).
 12. The method as claimed in claim1, wherein a thickness of the second insulating layer is greater thanabout 500 Å and less than about 1.5 times the thickness of the firstinsulating layer.
 13. The method as claimed in claim 1, wherein thecontact has a trapezoidal section.